1. Field of the Invention
The present invention relates to an electrical cable, and typically but not exclusively applies to the electrical cables used in aeronautics, for example on board airplanes.
2. Description of Related Art
This type of electrical cable must meet many criteria if it is to be used in aeronautics, especially when it is to be subjected to high voltages, about 230 V AC or about 1270 V DC, and when it is to be located in depressurized zones.
These relatively high voltages, in combination with aeronautics-related factors, such as moisture, high temperatures and low pressures, may generate partial discharges (PDs) in electronic equipment such as electrical cables. Partial discharges, which are minuscule electrical arcs in the electrical insulator of the cable, cause, over time, the electrical insulator to degrade, which may lead to it rupturing.
Other criteria may also be taken into account such as the weight and diameter of said cable, which must not be excessive, and the markability of said cable in order, when required, to allow it to be identified.
In the prior art, it is known to equip airplanes with hook-up wires, these wires comprising a conductive element surrounded by a 0.017 to 0.065 mm-thick first polyimide layer, itself surrounded by a 0.1 to 0.22 mm-thick polytetrafluoroethylene PTFE layer for nominal conductive cross sections ranging from 0.15 to 120 mm2. However, for such hook-up wires the applied voltage is about 115 V.
Document EP 1 498 909 relates to a multilayer insulation having the function of insulating and/or protecting electrically conductive hardware such as aeronautical cables. This insulation comprises, in succession, around the electrical element to be protected, a first polyimide (PI) layer, a second tetrafluoroethylene/perfluoro(alkylvinylether) (PFA) copolymer layer, and optionally an external polytetrafluoroethylene (PTFE) layer. The thickness of the PI layer ranges from 8 to 150 μm and the thickness of PTFE ranges from 1 to 200 μm. However, the resistance to partial discharges of an electrical cable surrounded by this multilayer isolation is also not optimized for high voltages, such as voltages of about 230 V AC or about ±270 V DC.